Central venous access devices, which are essential in the care of many oncology patients, often become occluded with fibrin. Although this obstruction can usually be removed with routine instillations of urokinase, this method sometimes is unsatisfactory. This project is studying the efficacy of continuous (1- to 12-hour) infusions of low-dose urokinase to restore function to access devices refractory to the routine urokinase instillations. Forty-six patients have been accrued. Treatment has been successful in approximately 80 percent of cases. (Protocol #93-CC-0135)